Overview
Emboli may consist of either formed elements such as blood clots, platelet aggregates, or other particulate matter such as pieces of atherosclerotic plaque, fat, or, they may be gas bubbles introduced to the blood vessels through injection, surgical techniques, cavitation at prosthetic valves, or decompression or compression to lower or higher atmospheric pressures. The consequence of arterial emboli may be such pathological conditions as ischemia of an organ or limb, impairment of function, transient ischemic attacks or stroke. The consequence of venous emboli may be pulmonary embolism, pulmonary hypertension, impairment of the function of the heart or lungs or passage to the arterial circulation to produce arterial embolic consequences.
Because the intensity of the ultrasound reflected from emboli exceeding a minimum size is greater than that reflected from normal moving blood, the emboli produce a transient increase in the amplitude of the Doppler shift frequency component corresponding to the velocity component of the emboli parallel to the ultrasound beam.
At present, there exists no other means, either noninvasive or invasive, which allows for the routine dynamic observation and characterization of such transient embolic events.